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JAMB Physics 2020 Paper

Question : 32

Total: 38

The fiqure above represents a block-and-tackle pulley system on which an effort of W Newtons supports a load of 120.0N. If the efficiency of the machine is 40 $^{\circ}$ , then the value of W is

28.0N
48.0N
288.0N
50.0N

Validate

Solution:

Concept:

Efficiency compares the useful work output to the work input using the velocity ratio of the pulley system.

Explanation:

From the block-and-tackle system, the velocity ratio is

V.R = 6

Load

= 120.0\,N

and effort

= W

Mechanical advantage is

M.A = \frac{\text{load}}{\text{effort}} = \frac{120}{W}

Efficiency is given by:

\text{Efficiency} = \frac{M.A}{V.R} \times 100\%

Substitute the values:

40 = \frac{\frac{120}{W}}{6} \times 100

40 = \frac{120 \times 100}{6W}

40 = \frac{2000}{W}

W = \frac{2000}{40} = 50.0\,N

Answer:

The value of

W

50.0\,N

, which is option D.

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